Final answer:
The largest amphibious operation ever assembled was Operation Overlord (D-Day) which took place on June 6, 1944 in Normandy, France.
Step-by-step explanation:
The largest amphibious operation ever assembled to conduct minesweeping, shore bombardment, and transport of supplies and troops was Operation Overlord (D-Day). On June 6, 1944, American, British, and Canadian forces launched this operation in Normandy, France. It involved over 5,000 landing and assault craft, about 160,000 men, and became the largest amphibious assault in history.